“It is going to take an incredibly strong Republican to defeat the Democrats as they look to defend this open seat that has been in their control for over three decades. Thankfully, Iowa Republicans have such a candidate in Joni Ernst,” Romney said in a mailer endorsing Ernst, according to the Des Moines Register.

“As a mother, soldier and proven conservative, Joni has the kind of experience, skill set and discipline it will take to not only win this important seat, but to also take Iowa values to help turn around the mess in Washington.”

Romney’s endorsement could help Ernst stand out in the crowded, six-candidate GOP field seeking the open Senate seat in the Hawkeye State. The seat is open this cycle because Sen. Tom Harkin, D-Iowa, is retiring.